Saline short-term shock and rapid recovery on anammox performance

Anaerobic ammonia oxidation (anammox) is an environmental-friendly biological nitrogen removal process, which has been developed as a promising technology in industrial wastewater treatment. However, anammox nitrogen removal under high saline conditions still faces many challenges. This study investigated the performance of anammox sludge under saline short-term shock and the strategy of rapid recovery. Salinity concentration, saline exposure time, and NaCl/Na₂SO₄ ratio were selected as three critical factors for short-term shock. The activity inhibition of anammox sludge were tested by using response surface methodology (RSM). Our results showed that, compared with the NaCl/Na₂SO₄ ratio, the salinity concentration and saline exposure time were the significant factor causing the anammox inhibition. The addition of glycine betaine (GB) in moderate amounts (0.1-5 mM) was found to help anammox to resist in relative low saline shock intensities (e.g., IC₂₅ and IC₅₀), with the activity retention rate of 94.7%. However, glycine betaine was not worked effectively under relatively high saline shock intensities (e.g., complete inhibition condition). Microbial community analysis revealed that Brocadiaceae accounted for only about 7.6%-13.2% at inhibited conditions. Interestingly, 16S rRNA analysis showed that the abundance of activated Brocadiaceae remarkably decreased with time after high-level saline shock. This tendency was consistent with the results of qPCR targeted hzsA gene. Finally, based on quorum sensing, the anammox activity was recovered to 93.5% of original sludge by adding 30% original sludge. The study realized the rapid recovery of anammox activity under complete inhibition, promoting the development and operation of salt-tolerant anammox process.